1. Field of the Invention
The present invention relates to a method of lubricating a sliding portion between a cylinder and a piston of a two-cycle internal combustion engine configured to prevent blow-by of an air-fuel mixture in a combustion chamber, thereby enhancing a fuel consumption and an exhaust purifying performance.
2. Description of the Relevant Art
FIGS. 9 and 10 show a prior art two-cycle internal combustion engine disclosed in Japanese Patent Laid-open No. Hei 10-325313. FIG. 9 is a longitudinal sectional view of an essential portion of the engine and FIG. 10 is a horizontal sectional view of an essential portion of the engine.
In the two-cycle internal combustion engine of this type, air is sucked and compressed in a crank chamber and the scavenging is performed by the compressed air; after the scavenging only by air is ended, a high compression gas is charged from a combustion chamber 013 into a chamber portion 020 provided adjacently to a cylinder 005; and an air-fuel mixture is formed by the high compression gas and fuel and is injected into the combustion chamber 013.
In these figures, reference numeral 003 designates a cylinder block; 005 is a cylinder provided in the cylinder block 003; and 020 is a chamber portion provided adjacently to the cylinder 005. The cylinder 005 is connected to the chamber portion 020 via a communication passage 030. A rotary valve 040 for opening/closing the communication passage 003 is provided in a mid portion of the communication passage 030.
The communication passage 030 has one cylinder side passage portion positioned on the cylinder 005 side from the rotary valve 040, and two chamber portion side passage portions positioned on the chamber portion 020 side from the rotary valve 040. In the figures, reference numeral 031 designates a cylinder side opening of the communication passage 030, and reference numeral 032 designates each of two chamber portion side openings of the communication passage 030. A fuel injector (not shown) is mounted in each of two mounting holes 036 formed at ends of intermediate portions of the two chamber portion side passage portions of the communication passage 030.
The rotary valve 040, disposed in such a manner as to cross the communication passage 030, is composed of a first control valve 041 configured as a deeper cutout and a second control valve 042 configured as a shallower cutout. The second valve 042 is disposed in front of the first control valve 041 in the rotational direction while being continuous to the first control valve 041. The first control valve 041 controls the flow of a high compression gas, and the second control valve 042 controls the flow of an air-fuel mixture.
The switching from the flow of an air-fuel mixture to the flow of a high compression gas is dependent on a balancing relationship between a pressure in the combustion chamber 013 and a pressure in the chamber portion 020. This is because the communication passage 030 is commonly used for charging the high compression gas in the chamber portion 020 and for injecting the airfuel mixture from the chamber portion 020. To be more specific, when the pressure in the combustion chamber 013 becomes higher than the pressure in the chamber portion 020, the flow in the communication passage 030 is switched from the flow of the air-fuel mixture into the flow of the high compression gas. Nearly at this time, the flow control by the rotary valve 040 is shifted from the flow control of the air-fuel mixture by the second control valve 042 to the flow control of the high compression gas by the first control valve 041.
In the figures, reference numeral 014 designates each of four scavenging passages, and 021 also designate a scavenging passage; 015 is a cylinder side opening of the scavenging passage 014, and 022 is a cylinder side opening of the scavenging passage 021; 016 is an exhaust passage and 017 is a cylinder side opening of the exhaust passage 016; and 013 is a combustion chamber.
Referring to FIG. 10, two lubricating oil supply holes 050 for lubricating a sliding portion between the cylinder 005 and the piston 006 are provided on both sides of the communication passage 030. Cylinder side openings 051 of both the lubricating oil supply holes 050 are formed in the inner wall surface of the cylinder 005 at positions located on both sides of the cylinder side opening 031 of the communication passage 030 in the circumferential direction and located between the opening 031 of the communication passage 030 and the scavenging openings 015 in the height direction. Lubricating oil, which is fed in the lubricating oil supply holes 050 by an oil pump (not shown) connected to outer openings 052 of the lubricating oil supply holes 050, flows from the openings 051 of the lubricating oil supply holes 050 into the cylinder bore 005.
Two lubricating oil supply holes 055 having openings 056 are provided on both sides of the cylinder side opening 017 of the exhaust passage 016 as needed. Lubricating oil, which is fed in the lubricating oil supply holes 055 by an oil pump (not shown) connected to outer openings 057 of the lubricating oil supply holes 055, flows from the openings 056 of the lubricating oil supply holes 055 into the cylinder bore 005.
In the above-described prior art internal combustion engine, an air-fuel mixture containing gasoline as fuel is injected from the cylinder side opening 031 of the communication passage 030. The gasoline contacts a portion near the opening 031 of the communication passage 30 of the inner all of the cylinder 005, and a portion facing to the opening 031 of the communication passage 030 of the outer peripheral surface of the piston 006. As a result, the lubricating oil adhering on the inner wall of the cylinder 005 and on the outer peripheral surface of the piston 006 is often carried away or washed away by the gasoline. As a result, according to the prior art engine, it is difficult to maintain the lubricating performance, and to prevent lubricating oil adhering particularly on a portion on the communication passage side of the piston 006 from being all carried away by gasoline. Therefore, in accordance with the prior art, it has been necessary to supply an excessive amount of lubricating oil from the lubricating oil supply holes 050.
It is an object of the present invention is to solve one or more of the drawbacks of the prior art""s internal combustion engines. To this end, the present invention provides a lubricating system for a two-cycle internal combustion engine, which is capable of sufficiently and effectively lubricating the engine by supplying a smaller amount of lubricating oil.
According to the present invention, there is provided a method of lubricating a two-cycle internal combustion engine which includes a combustion chamber, a chamber portion, a communication passage provided between the combustion chamber and the chamber portion. One end of the communication passage is opened in an upper portion of a cylinder as a constituent component of the combustion chamber, and a control valve for controlling the opening/closing of the communication passage is provided.
A high compression gas is charged in the chamber portion and an air-fuel mixture is injected from the chamber portion into the combustion chamber via the communication passage by way of the high compression gas stored in the chamber portion.
A lubricating system in accordance with the present invention is characterized as follows:
(1) A lubricating oil supply hole is provided in the cylinder. The lubricating oil supply hole has a cylinder side opening positioned in the same direction as the direction in which a cylinder side opening of the communication passage is positioned, as seen from the center line of the cylinder. With this configuration, since the piston (or the piston ring) passes through the opening of the lubricating oil supply hole immediately before and after it passes the opening of the communication passage in the upward or downward stroke of the piston, even if lubricating oil adhering on the wall surface of the piston (or piston ring) is carried away by fuel, lubricating oil can be immediately, newly supplied thereto.
(2) In addition to the configuration of the lubricating method described in the item (1), the cylinder side opening of the lubricating oil supply hole may be positioned under the cylinder side opening of the communication passage. With this configuration, it is possible to reduce the influence of heat and/or pressure in the combustion chamber exerted on the lubricating oil supply hole in the downward stroke of the piston.
(3) In addition to the configuration of the lubricating method described in the item (1), the cylinder side opening of the lubricating oil supply hole may be provided between the lower edge of the cylinder side opening of the communication passage and a position at which a piston ring of a piston is located when the piston is moved down to the bottom dead center. With this configuration, since lubricating oil can be supplied not only to the wall surface of the piston, but also to the piston ring itself, it is possible to effectively supply lubricating oil to the sliding surface of the sliding portion between the cylinder and the piston.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.